1. Field of the Invention
The present invention relates to an electronic component having a tin alloy plating film, and more particularly to an electronic component having a lead-free tin alloy plating film.
2. Description of the Related Art
Tin alloy plating films have been used in various electronic components. FIG. 1 shows a conventional laminated ceramic capacitor 5 as one example of such electronic components. The laminated ceramic capacitor 5 comprises a laminated ceramic body 3 in which dielectric layers 1 and internal electrodes 2 are alternately stacked and a pair of external electrodes 4 are electrically connected to the internal electrodes 2. Each of the external electrodes 4 includes a Ag electrode 4a as a foundation layer, a Ni electrode 4b provided on Ag electrode 4a as an intermediate layer and a Sn electrode or a Sn--Pb alloy electrode 4c provided on the Ni electrode 4b as an outermost layer.
The Ag electrode 4a is formed for electrical connection to an internal electrode, and the Ni electrode 4b is formed to prevent corroding of the Ag at the time of soldering or the generation of whiskers. The Sn electrode or Sn--Pb alloy electrode 4c is formed in order to promote the wettability of solder at the time of soldering.
The conventional electronic components represented by the laminated ceramic capacitor 5 have the following problems when the Sn electrode or Sn--Pb alloy electrode is formed. Sn plating films are likely to generate whiskers. On the other hand, the Sn--Pb alloy electrode includes Pb which is a regulated substance, and is therefore necessary to be replaced in view of environmental problems.
In addition, when the Sn or Sn--Pb alloy outermost electrode is formed by electrolytic plating the Ni electrode is usually formed in advance by electrolytic plating. However, the Ni plating liquid sometimes contaminates the Sn or Sn--Pb plating bath adversely. This results in degradation of the adhesive strength of the plating film and the poor quality of the obtained plating film.
In order to solve this problem, it is necessary to perform a cleaning process after the Ni plating process, thereby preventing residual Ni plating liquid from being brought into the plating bath of the Sn or Sn--Pb. In addition to this countermeasure, it might be necessary to renew the plating bath of Sn or Sn--Pb more frequently based on the number of uses of the plating bath. As a result, the number of process steps and production controls are increased. This results in an increase of the production cost.
For the forgoing reasons, there is a need for an electronic components having a plating film which includes no Pb, causes no whiskers and prevents corrosion of Ag at the time of soldering, as well as promotes wettability of solder.